Known more for his size than his intellect, Moloch is a massive, lumbering Oni originally from the Netherrealm carrying a massive chained orb. During Quan Chi's escape from Scorpion in the Neatherrealm, the sorcerer ran across Moloch and his fellow demon Drahmin with an offer: freedom from the Neatherrealm if they protect Quan Chi. Both took up the bargain, but when time came to escape through a portal, Quan Chi bailed on them, and the resulting jumping into the portal brought them to Outworld instead.
After a couple of misadventures encountering Cyrax and Li Mei, the Oni duo came across Shang Tsung, who took them as fearsome warriors and an insurance policy should Quan Chi double cross the other half of the Deadly Alliance. Eventually, after once again helping Quan Chi by hurling a vengeful Scorpion into the palace's Soulnado, the two were set free. They were left unharmed by the ensuing battle against Onaga or they escape, as both Moloch and Drahmin show up in the Battle of Armageddon.
Unfortunately for Moloch in the rebooted timeline, Quan Chi seems to have killed him, and walks around with his severed head as his personal trophy.
Blue Oni: Inverted—While he is colored blue, he is much more primal and vicious than Drahmin (if the latter is wearing his mask). Both are still Red in the overall scale.
Drahmin was an Oni Tormentor wandering the 5th plane of the Neatherrealm looking for souls to torment. Alongside Moloch, he pledged service to Quan Chi when they encountered each other. With Drahmin's help, Quan Chi was able to locate and activate a portal that led them to escape, but in the ensuing chaos when Scorpion showed up, Quan Chi and the Oni duo were separated.
What happened after Drahmin and Moloch escaped Shang Tsung's palace was unknown, but Drahmin eventually found his way back to the Neatherrealm, where he was soundly defeated by a wandering Taven.
Cool Mask: Which he removes while switching styles.
His non-canon ending in DA implies that he became a higher being like Quan Chi after entering the inner sanctum located in Quan Chi's fortress.
Before Kano and the Black Dragon Clan became feared criminals, they were part of the Red Dragon Clan and one of their leaders named Mavado. If Kano used brute force and scare tactics, Mavado used discipline and superior intellect to achieve his goals. This vicious pitiless crime lord engineered the destruction of the original Black Dragon clan by planting a mole inside the Outworld Investigation Agency, and would eventually soundly defeat Kabal and acquire his trademark hookswords.
When Mavado was contacted by the Deadly Alliance as a potential ally, he gladly accepted the proposition. As an enforcer for the Deadly Alliance, he was able to defeat Kenshi, instruct his mole to further sabotage the Outworld Investigation Agency, and capture Kano. He would eventually be defeated by a vengeful Kabal, but return in time for the Battle of Armageddon, his hatred for the Black Dragon still burning.
Back from the Dead: Kabal supposedly killed him after Deadly Alliance to get his Hookswords back (and to return the favor for nearly killing him. Not only does he return without explanation, but he still has the Hookswords (though he may have simply acquired a new pair of his own).
Foil: Could be considered one to Kano. Whereas Kano seems to rely mainly on scare tactics and brute force, Mavado values discipline, superior intelligence, and good strategy to win a fight and enforces this among his men.
Kenshi was a talented martial artist severely lacking in humility, until one day he was approached by a man named Song (actually Shang Tsung in disguise) with a tempting offer: unseal an old well which could only be opened by those of his bloodline, so that Kenshi might gain an immensely powerful sword sealed within. The well was actually the resting place of Kenshi's ancestors, and when he unsealed it, the powerful mystic light that emanated from within painfully blinded him. Of course, it was all an evil plan by Shang Tsung, who absorbed the souls of Kenshi's warrior ancestors and let him to rot, laughing all the way.
However, at the bottom of the well, Kenshi DID find a source of power: Sento, the mystic sword which was infused with power from his ancestors. Determined to kill Shang Tsung and atone for his arrogance, Kenshi retrains his remaining senses to superhuman levels and becomes a swordsman without equal, seeking to free his ancestors' souls by making Shang Tsung eat his blade.
Amazing Technicolor Population: His skin was somewhat grey in his debut (only in his default costume; his alternate had a more normal hue), although this was fixed from Deception onward.
Arrogant Kung-Fu Guy: Was one of these before the series began. Shang Tsung uses this to his advantage, tricking Kenshi into releasing the souls of his ancestors for his consumption.
Attack Reflector: Gains a move allowing him to redirect projectiles with a slash of his katana in 9.
Blinded by the Light: Opening the Well of Souls where his ancestors resided permanently did this to him.
Blind Justice: Heh... He even has a combo in the DA-D-A trilogy named this, no doubt a nod to one of his inspirations, Daredevil.
Disability Superpower: Almost exactly like Daredevil. In the DA-D-A trilogy, it also gives him immunity to Sonya and Kira's Kiss of Death moves, which aim for the eyes. In 9, however, he's still stunned by Stryker's X-Ray opener (blinding the opponent with a flashlight).
The Drifter: A lone warrior by nature, he turns down the offers of allies Sonya and Sub-Zero (to permanently join the OIWA and join the Lin Kuei, respectively) and instead traverses the lands, striking down several criminal organizations in the cover of night.
Meaningful Name: His name is Japanese for "swordsman." Kenshi is also referred to as "the Sword Saint" in the Konquest mode of Deadly Alliance, which is the English equivalent of the Japanese word kensei.
Mind over Matter: Actually an inherent ability of his (according to DA's Konquest Mode, Ermac merely taught him more complex techniques like the Telekinetic Slam).
Missed the Call: Deception's Konquest mode reveals that Kenshi had hoped to enter the first game's tournament to enact revenge on Shang Tsung. Three guesses as to how that turned out.
When Quan Chi and Shang Tsung needed a new palace built to house the Soulnado, they tasked Kano with looking after some slaves from a nearby village to build it. One of these slaves, Li Mei, managed to get the better of him and impressed the Deadly Alliance. They offered Li Mei the chance to fight in the Deadly Alliance tournament to free her village. This however turned out to be bogus, as her reward for "winning" was having her soul transferred into one of the undead soldiers of the Dragon King's army. Last minute intervention by Bo'Rai'Cho however managed to partially halt the process, but at the cost of Li Mei having a few personality alterations.
Rescued, she rejoined the fight against the resurrected Onaga, and the eventual Battle of Armageddon.
Absolute Cleavage: As you can see to your right, her first outfit in Deception has this. It's also present, to varying degrees, in her other outfits.
Plucky Girl: Let it be said that when she fought back against the foot soldiers under the command of the Deadly Alliance, she most likely would have defeated Kano had it not been for Quan Chi's intervention.
Xenafication: In Deception. Hardened by her ordeals and near death experience in Deadly Alliance, Li Mei becomes less sweet and more of a battle-oriented warrior. This is reflected by her alternate costume; as Bo' Rai Cho was not fully successful in saving Li Mei, she took on some of the aspects of the Dragon King's soldiers, reflecting the partial corruption of her soul. This also comes with a price; as Li Mei is technically one of Onaga's soldiers, she is magnetically drawn towards him, culminating in her non-canon Face-Heel Turn in her Deception ending.
Mavado, leader of the Red Dragon Clan, sent in one of his most trusted soldiers into the Outworld Investigation Agency to sabotage it from within. That soldier was Hsu Hao, who was instrumental in wiping out the Black Dragon Clan for the benefit of Mavado. This Mongolian grappler is unquestionably loyal to his leader, and has a cybernetic implant that replaces his heart to augment his body strength. After Mavado started working for the Deadly Alliance, he ordered Hsu Hao to destroy the OIA's underground base and means to travel to Outworld, and made his way back to the realm to rendezvous with his superior. His new orders were sent from Quan Chi through Mavado to kill Shang Tsung.
He was on his way when he ran across a vengeful Jax, who did not take his betrayal lightly and seemingly killed him by ripping the cybernetic heart off his body. Through unknown means, he survived, and joined the Battle of Armageddon.
The Mole: Sent by Mavado to pose as a member of the Chinese secret military and aid the Special Forces in catching and killing Black Dragon members. This allowed Hsu Hao to get close enough to the OIWA and destroy it and its portal system after the Red Dragon's rival clan had been wiped out.
Nice Hat: If his alt. is any indication, he's bald underneath.
Wrestler in All of Us: His second fighting style in DA is Wrestling and one of his throws is a backbreaker.
Nothing much is known about this seemingly normal martial artist-turned motion capture specialist, but he is known to be a master of several styles of martial arts and is hired by Johnny Cage to work on some of his movies. For reasons unknown he would be involved in the conflicts against the Deadly Alliance and Onaga, and show up at the Battle of Armageddon.
Fish out of Water: The most normal character in the game. That he can throw energy balls and telekinetically lift his foes speaks volumes about the Mortal Kombat version of Earth.
Nitara is introduced as a vampire who spent ages in Outworld trying to find a mystical orb that would separate Outworld from her home realm of Vaeternus. The orb however was submerged under molten lava and inaccessible to her. A chance encounter with Cyrax improved he fortunes, and she began work on manipulating the cyborg ninja to achieve her goals. She first met with a mentally deranged Reptile, who pledged his service to her after presenting a sword from Reptile's home realm Zaterra. She manipulated Reptile into attacking Cyrax and destroy his only means of traversing the realms. After Reptile fled from Cyrax bombs, Nitara approached Cyrax with a deal: obtain the orb from the lava, and she will send him back to Earthrealm. Both held up their end of the bargain, and they were sent back to their respective realms and Vaeternus was separated from Outworld.
The peace was short lived, as soon after, many vampires in the realm were slaughtered. The marks of the wounds were discovered to orignate from a weapon that was wielded by the demon Ashrah. Nitara, as ordered by her superiors, joined the Battle of Armageddon to slay Ashrah once and for all.
Teleporters and Transporters: The gemstone around her neck allows Nitara to freely traverse the realms. With a magical incantation, she can also send other characters to their home realms, as seen with Cyrax in Deadly Alliance.
Vampiric Draining: Her throw and Fatality involve sucking the blood out of her opponent's neck, with the former actually restoring some of her health when used.
Wings Do Nothing: Averted. She actually uses them for quick escape maneuvers in her moveset in Deadly Alliance, but this feature (along with taunts) was largely removed by the time of Armageddon.
After Sub-Zero became the new Grandmaster of the Lin Kuei, he began looking for new students. One of these students is Frost, who also had ice powers. Sub-Zero took her in as his protege and began training her, but as she grew in strength, she also grew in arrogance. She, alongside her Sifu, joined the battle against the Deadly Alliance, but she did not get along with the others, most especially Sonya.
Once in Outworld, Frost immediately betrayed Sub-Zero, aspiring to become Grandmaster herself. The power of the Dragon Amulet that granted Sub-Zero his status, however, proved too powerful for her and froze her to death. She was laid to rest by Sub-Zero in a Cryomancer temple in Outworld, which revealed that both Sub-Zero and Frost are descended from these ice wielders. She awoke some time afterwards and returned to the Lin Kuei temple awaiting Sub-Zero's return with the intent of killing him. With a hint of insanity in her, she was no match for her former Sifu and was promptly frozen again, only to be freed by an unsuspecting Taven on his quest. She escaped, still in a delirium, and joined the Battle of Armageddon with only one goal: killing Sub-Zero.
An Ice Suit: Shows a bit more skin than the male variant, but still modest for a female Cyromancer.
Anime Hair: Lampshaded in DA, which states that she uses a brand of hair gel called Arctic Hold◊ to keep her hairdo intact.
Arrogant Kung Fu Gal: Sub-Zero hoped that tutelage would teach Frost humility. As her skills increased, so did her arrogance and haughtiness, even towards her sifu. This is part of the reason she came to butt heads with Sonya.
Mysterious Past: To date, nothing is known about Frost before she joined the Lin Kuei.
The Rival: To Sonya, and the feeling is mutual, but neither has ever explained why.
Sanity Slippage: Upon being accidentally released by Taven, Frost is seen to be clearly delusional, hallucinating that she sees Sub-Zero everywhere. She eventually recovers, although her hatred of her former sifu has not subsided.
She-Fu: Unlike her sifu, who slides around Iceman-style to escape from sticky situations in Deadly Alliance, Frost prefers to perform backflips. Subverted, however, in that several of the male characters (such as Shang Tsung and Hsu Hao) also use backflips to escape.
Spontaneous Weapon Creation: Same as Sub-Zero, although since she's weaker and less experienced than he, Frost can only harness her Fa Jing in the form of twin daggers as opposed to Sub-Zero's Kori Blade.
The elemental only known as Blaze was created by an Edenian sorceress to oversee the strength of all the kombatants of the various realms and prevent a seeming Armageddon. At a certain point however, Blaze was captured by a group of holy men that worshiped the deceased Onaga and corrupted Blaze into protecting Onaga's egg for an undisclosed amount of time. He was eventually freed, but discovered that the kombatants have become too numerous and powerful to handle and that Daegon, one of the chosen Edenians to partake in the quest to prevent Armageddon, was corrupted by a premature awakening.
Blaze then awoke Taven, where, after his quest, he revealed his true purpose to the Edenian. As the Battle of Armageddon raged, Blaze and Taven fought in Mortal Kombat atop a pyramid to prevent the future of the realms and the coming or delay of Armageddon.
Ascended Extra: He started off as a background sprite in Mortal Kombat II; in Deadly Alliance he was a secret character, and in Armageddon, he's the final boss and MacGuffin, revealed to be the linchpin of a millenia-old plot to prevent the apocalypse.
The Corruption: Being forced to carry Onaga's egg may be the reason for his appearance in Armaggedon.
Armageddon's Konquest mode, however, shows that Blaze assumes his DA appearance and only morphs into his Armageddon depiction during the great battle in Outworld, most likely so that he can be in a suitable fighting form for those who climb up the pyramid and attempt to take the power of Argus. However, his corruption by the holy men is the reason that Argus' plan to prevent Armageddon backfires, strengthening all the warriors instead of killing them or nullifying their powers.
Eldritch Abomination: Though he has an origin story, his personal motives are quite enigmatic. Very Lovecraftian in that way.
This fat, alcoholic, flatulent Outworld denizen is renowned as a martial arts master of incredible ability. Not only was it suspected that he brought Drunken Boxing to Earthrealm, he trained renowned heroes, including Shujinko and Liu Kang. As he was from Outworld, he could not participate in Mortal Kombat himself because he would win in the name of Shao Kahn. After Liu Kang won the first tournament, he retired. But Liu Kang's death and the rise of the Deadly Alliance prompted the old master to take up arms, joining Raiden's forces and training Kung Lao.
After the Deadly Alliance's defeat and the resurrection of Onaga, he rescued Li Mei from having her soul transferred and rejoined the remaining kombatants to fight Onaga, and would join the Battle of Armageddon.
Acrofatic: In fact, he uses Sumo as one of his fighting styles in Armageddon.
The Alcoholic: He even carries a gourd with him so that he can take a swig of his drink as a victory celebration.
Been There, Shaped History: Since he frequently travels between his native Outworld and Earthrealm to offer his teachings to others, he's responsible for the creation or refining of several Real Life martial arts. For example, after he was defeated by Miyamoto Musashi, Bo' Rai Cho would help Muso Gonnosuke improve his jujutsu by using a four-section staff instead of a six-section one. It's even speculated that he was the one who brought the fighting style of Drunken Boxing to Earthrealm.
The Obi-Wan: It's stated that he prefers to train students instead of directly applying his fighting skills. This is partially because he's a native of Outworld, thus meaning that if he were to win a Mortal Kombat tournament, he'd be sealing Earthrealm's fate instead of saving it. Three of his students are characters in the franchise: Kung Lao, Li Mei, and Liu Kang.
Physical God: He becomes a god in his non-cannon ending to Armageddon.
Simple Staff: His Weapon of Choice is a four-foot jō staff. (The Konquest Mode of Deadly Alliance claims that he aided the samurai Muso Gonnosuke in developing the fighting style associated with this weapon.)